Clinical studies to date have not determined the optimal degree of hemodilution during cooling prior to hypothermic low-flow cardiopulmonary bypass and total circulatory arrest used to support vital organs during reparative open heart surgery in infants. The purpose of the present pilot study is to provide data for a future prospective randomized clinical trial comparing neurologic and developmental outcome of two strategies of hematocrit management during the cooling phase of cardiopulmonary bypass, prior to circulatory arrest or low-flow, in infants and children undergoing reparative open heart surgery. Our goals will be pursued in a prospective, randomized, single-center trial. The treatment strategies will be compared with respect to neurologic parameters. Neurologic and developmental outcomes will be assessed at 12 months in those patients who live locally.